This invention relates to throttling devices or valve trim as part of conventional control valves where dissipation of moderate pressure differentials are desired, especially with natural gas or steam as fluid to be handled by the valve.
Concern for environmental noise control tends to exclude conventional valves with their solid plugs and seatring combinations due to their high inherent aerodynamic noise levels whenever the ratio between inlet and outlet pressure across the valve exceeds 2:1, i.e. sonic throttling velocity exists. While the best method for noise reduction is a combination of multiple throttling stages in series (to reduce velocity) and a large number of throttling passages as, for example, described in my U.S. Pat. No. 3,908,698, there are many more moderate applications i.e. lower pressure differentials, where it is sufficient to increase the number of parallel throttling passages in order to obtain the desired noise reduction, usually in the order of 10 to 15 dB.
Accoustical energy, i.e. Soundpower, increases roughly as the 18th power of the flow area of a valve orifice but only to the 10th power of increase in mass flow. It is therefore easy to see that important noise savings can be made simply by keeping the orifice diameter constant and by accommodating the increase in mass flow through increase in the number of parallel orifices. For example, about 14 dB can be saved with a 64-fold increase in mass flow then, instead of employing a single orifice 8 times enlarged in diameter, 64 individual orifices of the same original diameter are used.
While the concept of multiple orifice trim is not new, the production of conventional state of the art devices is rather costly as it involves mechanically drilling a multitude of small holes into heavy sections of stainless steel plugs or cage members. The machining problems are aggravated by the fact that the surfaces to be drilled are curved, prohibiting the employment of multiple spindle drill heads.
My invention overcomes these difficulties by employing a stack of identical stampings which, when arranged in a certain circularly off-set pattern, automatically create an intricate network of vertical flow passages leading and feeding fluid to be controlled to a large number of individual small horizontal throttling passages from which fluid is allowed to expand into the downstream valve cavity.
After suitable arrangement of the plates against each other, the stack is either mechanically fastened or simply brazed together and against a solid valve plug disk or, in the female version against a solid seatring of conventional shape.
One other advantage of my invention lies in the fact, that each of the formed vertical flow passages can be considered as a separate pressurized cavity and, being substantially smaller than the single large cavity of a hollowed-out valve plug of conventional construction, will require less pressure carrying wall thickness than the latter, leading to weight savings and increased flow capacity in the vertical axis.
Additional great rigidity is derived from the honeycomb type network of ribs and circular wall sections, which overlap and, when brazed together, form a rigid structure.
These and other objects, features, and advantages of the present invention will be understood from the following detailed description.